Electric railway vehicle and an electric powering unit in particular for such a vehicle

ABSTRACT

An electrical power supply unit powers a load, in particular a transformer ( 8 ), from a power source ( 10 ) via electrical switchgear ( 14 ), in particular a circuit-breaker, and it includes an interference attenuator ( 16 ) of the ferrite type for attenuating interference due to switching. The attenuator ( 16 ) is placed between the power source ( 10 ) and the electrical switchgear ( 14 ), thereby contributing to reducing the extent of the interference significantly.

BACKGROUND OF THE INVENTION

The present invention relates to an electric rail vehicle provided withan electrical power supply unit.

It is common practice for such an electric vehicle, which may be alocomotive or a motor car or coach, to be powered via a catenarydelivering an AC working voltage.

The invention relates more particularly to such a vehicle that isequipped with a load, such as a transformer, and with an electricalpower supply unit for electrically powering said load from the catenary.The power supply unit conventionally includes electrical switchgear,such as a circuit-breaker, that protects the high-voltage AC circuits ofthe rail vehicle.

However, such a configuration suffers from certain drawbacks. Currentsappear whose gradients as a function of time are very steep. By way ofexample, when the AC normal working voltage is 25 kV at 50 Hz, currentsof 300 A are generated in about 5 ns. They give rise to interferencethat can damage, or, at the least, hinder proper operation of equipmentsituated in the vicinity-of the electrical switchgear, e.g. such ason-board control electronics.

In order to mitigate those drawbacks, an object of the invention is toprovide an electric rail vehicle equipped with an electrical powersupply unit that gives rise to low electromagnetic interference only, soas to guarantee that no damage is done to the structural integrity ofthe various items of electrical and electronic equipment with which thevehicle is provided.

SUMMARY OF THE INVENTION

To this end, the invention provides an electric rail vehicle, inparticular an electric locomotive, designed to be powered via acatenary, said vehicle including a load, in particular a transformer,and an electrical power supply unit for powering said load from saidcatenary, via electrical switchgear, in particular a circuit-breaker,said vehicle being characterized in that said power supply unit includesan interference attenuator of the ferrite type for attenuatinginterference due to switching.

According to an advantageous characteristic of the invention, saidinterference attenuator is placed between said catenary and saidelectrical switchgear.

The interference attenuator of the ferrite type for attenuatinginterference due to switching is known, for example, from JP-A-1 086 425and JP-A-4 322 024. In those documents, such an attenuator isconstituted by a cylinder made of ferrite and disposed around anelectrical line situated downstream from the electrical switchgear. Theferrite cylinder behaves as an inductor whose inductance increases withincreasing current frequency.

Because of the presence of metal members disposed in the vicinity of theconductor connecting the catenary to the circuit-breaker, straycapacitance forms in the vicinity of the roof of the rail vehicle andupstream from the switchgear. A transmission line constituting anelectromagnetic waveguide is created between said upstream straycapacitance and the switchgear proper.

On closing the switchgear, when a voltage is applied across the twoelectrodes of said switchgear, an electric arc strikes in it. Undercertain circumstances, in particular when the switching of theelectrical switchgear is based on vacuum “bottle” switching, saidelectric arc is extremely unstable, i.e. it is subjected to multipleinterruptions followed by corresponding re-strikes. Such arc instabilitycorresponds to successive breaks and re-makes that generateelectromagnetic interference resulting in steep current gradients whichcan damage or hinder proper operation of equipment situated in thevicinity of the electrical switchgear.

Because of the frequency, current, and voltage to which the electricrail vehicle is subjected, the interference attenuator of the ferritetype for attenuating interference due to switching is used for itsresistive portion, rather than for its inductive portion as in theabove-mentioned Japanese patent applications. By providing such aninterference attenuator, it is possible to reduce the steep currentgradients DI/DT generated on circuit-breaker closure, in particular whenthe attenuator is placed upstream from the switchgear. Rather thanmodifying the current oscillations, this contributes to preventing themfrom forming by reducing the value DI/DT, which is what can generatesuch oscillations.

In the invention, instead of seeking to filter out a steep currentgradient DI/DT initiated previously by the switchgear, the switchgear isforced to switch less rapidly, by influencing the physical establishingof the arc under a vacuum in the “bottle”.

The invention also provides an electrical power supply unit, inparticular for an electric rail vehicle, for powering a load, inparticular a transformer, from a power source via electrical switchgear,in particular a circuit-breaker, said power supply unit including aninterference attenuator of the ferrite type for attenuating interferencedue to switching, said power supply unit being characterized in thatsaid interference attenuator is placed between said power source andsaid electrical switchgear.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described below with reference to the accompanyingdrawings which are given merely by way of non-limiting example, and inwhich:

FIG. 1 is a summary diagram of an electric rail vehicle of theinvention, as provided with an electrical power supply unit;

FIG. 2 is a side view showing, in more detail, certain elements of theelectrical power supply unit of FIG. 1;

FIG. 3 is a perspective view of an attenuator for attenuatinginterference due to switching, which attenuator is part of theelectrical power supply unit of FIGS. 1 and 2;

FIG. 4 is a view partially in longitudinal section of the interferenceattenuator shown in FIG. 3;

FIG. 5 is a diagram of a laboratory experimental simulation of theelectrical switchgear of FIG. 1, and of its electrical environment; and

FIGS. 6, 7, and 8 show oscillograms of the upstream voltage, of thedownstream voltage, and of the current relating to the electricalswitchgear simulated in FIG. 5, respectively as not provided with aninterference attenuator, as provided with such an attenuator placeddownstream from the electrical switchgear, and as provided with such anattenuator placed upstream therefrom.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an electric rail vehicle, namely a locomotive given overallreference 2, and suitable for running on rails 4 connected to ground 6.

This locomotive 2 is provided with an on-board transformer 8 powered bymeans of a catenary 10 via a pantograph 12. The catenary 10 constitutesa power source, while the transformer is connected to the motor (notshown) of the locomotive.

Electrical switchgear, constituted by a circuit-breaker 14, and aninterference attenuator 16 for attenuating interference due to switchingand that is described in more detail below are interposed between thecatenary 10 and the transformer 8. The circuit-breaker is a vacuum“bottle” circuit-breaker that constitutes switchgear for coupling andprotecting the high-voltage AC circuits of the locomotive. Theattenuator 16 is disposed between the catenary 10 and thecircuit-breaker 14, i.e. it is placed upstream from saidcircuit-breaker.

The electrical circuitry on the roof of the locomotive 2, namely, inparticular the electrical lines interconnecting the roof equipment ofthe locomotive is the location where stray capacitance and strayinductance occur, constituting RLC-type circuits that can be excitedwhen the circuit-breaker switches.

The stray capacitance is represented diagrammatically in FIG. 1 byequivalent capacitors, namely an upstream equivalent capacitor 18 and adownstream equivalent capacitor 20, the terms “upstream” and“downstream” being used with reference to the circuit-breaker 14.

The stray inductance is represented diagrammatically in FIG. 1 byconnection chokes, namely an upstream choke 22 and a downstream choke24, also with reference to the circuit-breaker 14.

By interposing the attenuator 16, it is possible, with the roof of thelocomotive, to form a transmission line between the upstream capacitor18 and the circuit-breaker 14 at the working frequencies of thelocomotive. This transmission line defers the transfer of chargesbetween the capacitor 18 and the circuit-breaker 14, which reduces theamount of charge available for vacuum discharge, and reduces thegradient of the current as a function of time.

The body of the locomotive is represented by an equivalent LC circuitdesignated by reference 26 in FIG. 1, which circuit represents theresonance of the metal structure of the locomotive.

FIG. 2 shows the circuit-breaker 14 in more detail. For example thecircuit-breaker is as sold by ALSTOM TRANSPORT under reference ACB25-10.

The circuit-breaker is disposed in known manner on the roof of thelocomotive 2.

It stands on a base plate 28 and it is controlled via a relay stage 20.A lightning arrester 32, extending from the support plate 28, isconnected to the circuit-breaker 14. These elements are conventional.

The interference attenuator 16 is mounted on an insulator 34 whichitself stands on the plate 28. The attenuator 16 is formed around aconductor element 36 which, in this example, is constituted by a coppertube having two connections, namely an upstream connection 38 and adownstream connection 40. The upstream connection 38 is connected viameans (not shown) to the catenary 10, while the downstream terminal 40is put in connection with the circuit-breaker 14 via an electricalconnection 42 of the electrical braid type.

As shown more particularly in FIG. 4, the interference attenuator 16 ismade up of a plurality of annular ferrite elements 44, 46 which aredescribed in more detail below. The assembly of these elements 44, 46 isreceived in an insulating cylindrical housing 48 that is substantiallyclosed at its two ends and that is made of glass fiber, resin, or epoxy.The housing 48 is fixed to a channel-section base 50 via two hoops 52(see FIG. 3). The base 50 is itself secured to the top of the insulator34.

As shown more precisely in FIG. 4, the ferrite elements are disposed inpairs that are stacked up axially along the copper tube 36. Each pair offerrite elements is formed of a low-frequency element 44 disposed at theoutside periphery of the copper tube 36, and of a high-frequency annularelement 46 whose inside periphery is disposed in the vicinity of thelow-frequency element 44.

The housing 48 contains ten pairs of low-frequency and high-frequencyferrite elements, only the pairs of elements 44 & 46 and 44A & 46A beingreferenced in FIG. 4.

The concept of high-frequency and low-frequency ferrites is explainedbelow. Usually, a ferrite element is characterized by its relativepermeabilities, namely its real permeability μ′ and its imaginarypermeability μ″. μ″ increases with increasing frequency to reach amaximum at a “cutoff” frequency which, by convention, is referencedf_(c), and thereafter it decreases considerably. In the presentdescription, the ferrite elements 44 and 44A are referred to as being“low-frequency” because their cutoff frequency is lower than the cutofffrequency of the “high-frequency” ferrite elements 46 and 46A. Forexample, the cutoff frequency of the high-frequency ferrite elements maylie in the range 5 MHz to 20 MHz, while the cutoff frequency of thelow-frequency elements may lie in the range 0.5 MHz to 5 MHz.

For example, a low-frequency ferrite element is sold by Thomson CSF-LCCunder the reference B1-T-63000A, while a high-frequency ferrite elementis sold by Philips Components under the reference T107/65/253F4.

A mechanically-protective sheet 54 is interposed between the facingsurfaces of the low-frequency and high-frequency ferrite elements 44,46. For example, such a sheet is made of polyurethane-type resin and issold by LVA under the reference DAMIVAL 13518AW00. Another sheet 56 thatis similar to sheet 54 is interposed between the outside periphery ofthe high-frequency element 46 and the housing 48.

The invention makes it possible to achieve the above-mentioned objects.

By providing an interference attenuator of the ferrite type for theelectrical power supply unit that equips a rail vehicle, it is possibleto achieve a significant reduction in the interference to which thevarious items of electrical and electronic equipment of the rail vehicleare subjected. This reduction is particularly significant when theinterference attenuator is placed upstream from the electricalswitchgear.

FIG. 5 is a diagram of an experimental circuit implemented in thelaboratory and that reproduces in simplified manner the phenomenaoccurring on the roof of the locomotive 2 of FIG. 1.

The circuit-breaker 14 chosen for this experimentation was used in itsindustrial configuration. The equivalent electrical circuit diagram ofthis circuit-breaker was made up firstly of two stray-capacitancecapacitors, namely an upstream capacitor 14A and a downstream capacitor14B, the capacitors having capacitance respectively of 40 pF and of 60pF, and secondly of an inter-electrode capacitor 14C of variablecapacitance, and of two connection chokes 14D and 14E whose inductancewas 0.4 μH.

The circuit-breaker 14 was powered by means of a DC power source 58under a voltage of 20 kV at most and 1 mA. A load resistor 60 whoseresistance was equal to 10 MΩ was interposed between the source 38 andthe circuit-breaker 14. The experimental circuit diagram of FIG. 5 alsoreproduces the equivalent upstream capacitor 18 whose capacitance was 2nF, and the downstream choke 24, whose inductance was 25 μH.

At 62, the voltage immediately upstream from the circuit-breaker 14 wasmeasured, which voltage is referred to below as the “upstream voltage”.At 64 the voltage downstream from the circuit breaker or “downstreamvoltage” was also measured. Finally, downstream from the choke 24, thecurrent was measured at 66.

Once the capacitor 18 was charged, the circuit-breaker 14 was closed.The experiment was performed initially in the absence of any attenuatorfor attenuating interference due to switching, and the correspondingresults are given in FIG. 6. Then the experiment was implemented withthe circuit-breaker 14 being associated with an interference attenuator16 as described with reference to FIGS. 3 and 4. The resultscorresponding to the attenuator 16 being placed downstream from thecircuit-breaker 14, as shown in dashed lines in FIG. 5, are given inFIG. 7. FIG. 8 corresponds to the results of the experiment as conductedwith an interference attenuator being placed upstream from thecircuit-breaker 14, namely in accordance with the invention, as shown inchain-dotted lines in FIG. 5.

In all three of FIGS. 6 to 8, time is plotted along the x-axis on ascale of 20 ns per square. Starting from the top downwards, the y-axisgives the upstream voltage, referenced respectively 72A, 72B, and 72C inFIGS. 6, 7, and 8, then the downstream voltage, represented respectivelyby the references 74A, 74B, and 74C in FIGS. 6, 7, and 8, and finallythe current in the circuit-breaker, represented respectively by thereferences 76A, 76B, and 76C in FIGS. 6, 7, and 8.

The scale of the upstream voltages 72 is 2,000 volts per square, thescale of the downstream voltages 74 is 1,000 volts per square, and thescale of the currents 76 is 4 A per square.

With reference to FIG. 6, it can be observed that the current 76 isinitially zero prior to switching, it then increases at 78 under theeffect of circuit-breaker closure which causes an unstable arc tostrike. As a result, corresponding rising edges 80 and 82 are formedrespectively in the upstream voltage 72A and in the downstream voltage74A. Then, while having a very uneven profile, the current increases andthen decreases again to zero at 84. This causes major variations, at 86and 88, in the upstream voltage 72A and in the downstream voltage 74A,these variations being related to the successive interruption andre-striking of the arc.

The current 76A then describes a sinewave related to the resonance ofthe LC circuit 18, 24 of FIG. 5, and it then goes back, at 90, to itsinitial value of zero, thereby causing two additional variations, at 92and 94, in the upstream voltage 72A and in the downstream voltage 74A.

With reference to FIG. 7, it can be observed that the current 76B has aprofile that is more even than the profile 76A of FIG. 6. However,significant variations in the current over time can be observed. Inparticular, at 96, there is a strong increase in current due tocircuit-breaker closure. This results in the rising edges 98 and 100 inthe upstream voltage 72B and in the downstream voltage 74B. There arethus major current and voltage gradients which give rise to interferencefor the on-board electronics.

With reference to FIG. 8, which corresponds to the interferenceattenuator 16 being provided upstream from the circuit-breaker 14, thecurrent 76C has a profile that is significantly more even than theprofile 76B obtained by placing the attenuator 16 downstream from thecircuit-breaker 14. Only the rising edge 102 relating to the downstreamvoltage 74C remains significant.

By comparing FIGS. 6, 7, 8, it can be seen that, by using theinterference attenuator 16, it is possible to obtain current 76,upstream voltage 72 and downstream voltage 74 that are significantlymore even than those obtained without such an attenuator 16, inparticular when the attenuator 16 is disposed upstream from thecircuit-breaker 14. This is particularly advantageous because it makesit possible to limit the resonance effects of the roof circuits and ofthe locomotive.

The use of a plurality of ferrite elements is also advantageous. Theferrites become saturated as the current increases. The use of aplurality of ferrite elements whose permeabilities μ″ add together,makes it possible to impart satisfactory effectiveness to theinterference suppressor that is equipped with them, even for highcurrent.

It is also advantageous to distribute the ferrite elements in pairs,each of which is made up of elements whose cutoff frequencies aredifferent. This makes it possible to achieve optimum scanning of all ofthe frequencies generated on circuit-breaker closure. As the frequencyincreases, it is firstly the low-frequency ferrite element that iseffective, and then the high-frequency ferrite element takes over forhigher frequencies.

The use of annular ferrite elements that are fitted into one anothermakes the interference suppressor highly compact as a whole. Providingthe high-frequency element at the outside periphery of the low-frequencyelement is advantageous insofar as the high-frequency element becomessaturated for relatively low current, while the low-frequency elementexperiences such saturation for higher currents. In such aconfiguration, the high-frequency element is placed remote from thecentral conductor so that it is subjected to lower magnetic fields thatresult in it being saturated only to a lesser extent.

The above description is given with reference to a locomotive, but theinvention is also applicable to any electric rail vehicle, such as, forexample, a motor car or coach or a railcar.

What is claimed is:
 1. An electrical power supply unit in an electricrail vehicle, for powering a load which includes a transformer (8), froma power source (10) via electrical switchgear (14) which includes acircuit-breaker, said electrical power supply unit including a ferriteinterference attenuator (16) for attenuating interference due toswitching, wherein said ferrite interference attenuator (16) is placedbetween said power source (10) and said electrical switchgear (14). 2.An electric rail vehicle operative to be powered via a catenary (10),said vehicle comprising a load which includes a transformer (8), and anelectrical power supply unit for powering said load from the catenary(10), via electrical switchgear (14) which includes a circuit-breaker,wherein said electrical power supply unit includes a ferriteinterference attenuator (16) for attenuating interference due toswitching, wherein said ferrite interference attenuator (16) is placedbetween said catenary (10) and said electrical switchgear (14).
 3. Avehicle according to claim 2, wherein said ferrite interferenceattenuator (16) is made up of a plurality of ferrite elements (44, 46,44A, 46A) disposed around a conductor line (36) interconnecting saidcatenary (10) and said electrical switchgear (14).
 4. A vehicleaccording to claim 3, wherein said ferrite elements are distributedaxially in successive pairs (44, 46, 44A, 46A), each pair being made upof a high-frequency ferrite element (46, 46A) associated with alow-frequency ferrite element (44, 44A), said high-frequency ferriteelement having a cutoff frequency that is higher than the cutofffrequency of said low-frequency ferrite element.
 5. A vehicle accordingto claim 4, wherein the cutoff frequency of said high-frequency ferriteelement (46, 46A) lies in the range 5 MHz to 20 MHz, while the cutofffrequency of said low-frequency ferrite element (44, 44A) lies in therange 0.5 MHz to 5 MHz.
 6. A vehicle according to claim 4, wherein saidferrite interference attenuator comprises in the range two pairs offerrite elements (44 & 46; 44A & 46A) to twenty pairs of ferriteelements.
 7. A vehicle according to claim 4, wherein the two ferriteelements of each pair (44 & 46; 44A & 46A) are annular and fit into eachother, said high-frequency ferrite element (46, 46A) being disposed atthe outside periphery of the low-frequency ferrite element (44, 44A).